Astrology has little practical application, however, it still is scientific observation with some crazy computations :) it just happens their conclusions are very often imaginary. Likewise, religion is also a science, just sometimes with some crazy hypotheses, or "truths" that have no existence in the physical world or even claim to pertain to the physical world (ie, the afterlife). Hollow earth theory would be fringe science. Cooking is a science, at the mercy of the ever fallible sense of taste.
"If you do not desire some special traits, why is there even something such a eugenics?"
Eugenics is also the study of what traits are desirable. To know what are desirable genetic traits requires deep knowledge of many fields, which I don't presume to know, and don't trust the general population to know either.
"To me things such as eugenics is something best left behind, as it might lure man into selfish and destructive thinking."
You and I don't disagree on this, but I do believe if humanity ever reaches a certain level of scientific integrity, they most certainly can take the evolution of man in his own hands and do a better job than nature.
"Also, nature has got its wisdom and instead of manipulating it might be more wise to try to make the best of what is."
Just because it may be more wise to leave things to chance does not mean eugenics is not a science.
"You do contradict your own definition of science."
I'd like to know how. I consider science any attempt to understand something, even if it is blind men trying to describe what an elephant looks like by touch and there's no way they can form a good picture of the elephant by touching given how big it is. It is still scientific inquiry.